System for applying fluent materials

ABSTRACT

A system for applying .[.one-part thermal-cure.]. .Iadd.fluent .Iaddend.material, such as structural epoxy, includes apparatus for heating or cooling the epoxy to a temperature above or below ambient. A spirally coiled tube is suspended within a hollow enclosure by tube end fittings extending from axially opposed ends of the tube. An electrical heater and temperature sensor extend from opposed enclosure ends into the tube coils approximately centrally of the enclosure. The enclosure is filled with a heat transfer fluid that surrounds the coiled tubing. The fluid is connected through an inlet and outlet in the enclosure endwalls for circulation externally of the enclosure through a fluid chiller. A microprocessor-base controller receives input signals from the temperature sensor and a temperature adjustment mechanism, and provides outputs to the heater chiller and heater-exchange fluid pump and circulation valve, and to alarm mechanisms for indicating a high-temperature or low-temperature alarm condition.

.Iadd.This application is a RE of 07/23,630, Jul. 25, 1988, U.S. Pat.No. 4,890,573.

The present invention is directed to a system for applying or depositing.[.one-part thermal-cure.]. .Iadd.fluent .Iaddend.materials such asstructural epoxy, and more particularly to a device for controllablyheating or cooling the material to a preselected temperature above orbelow room temperature prior to material deposition.

It is a general object of the present invention to provide a materialapplication system of the described character that includes a materialheating and cooling device which obtains enhanced control of a materialtemperature, and in which the material is thoroughly heated throughoutits volume without internal temperature gradients or the like.

Another object of the present invention is to provide a material heatingapparatus for use in such a system which is sufficiently small as to bemountable on a robot arm adjacent to the application nozzle, and whichthereby obtains enhanced control of material temperature at theapplication nozzle without deleterious effects of heat loss or gainduring passage through intermediate conduits.

A further object of the invention is to provide a material heatingapparatus of the described character that is economical to assemble andreliable in operation over an extended lifetime.

The invention, together with additional objects, features and advantagesthereof, will be best understood from the following description, theappended claims and the accompanying drawings in which:

FIG. 1 is a fragmentary perspective view of a system for applyingthermal-cure materials in an automated production process in accordancewith a presently preferred embodiment of the invention.

FIG. 2 is a partially schematic and partially fragmented sectional viewof the material heating apparatus in FIG. 1; and

FIG. 3 is an end elevational view of the material heating apparatusillustrated in FIGS. 1 and 2.

FIG. 1 illustrates a system 10 for applying a bead 12 of structuralepoxy to the interior surface of a multiplicity of door panels 14passing in sequence along a conveyor 16. A robot arm 18 is positionedadjacent to conveyor 16 at the material application station, and ismovable in multiple degrees of freedom under control of a robotcontroller 20. To the extent thus far described, line 10 illustrated inFIG. 1 is entirely exemplary of an environment in which a system inaccordance with the present invention may be employed.

In accordance with the presently preferred embodiment of the invention,material to be deposited as bead 12 is applied by air-driven positivedisplacement high-volume high-pressure double-acting suction-assisteddouble elevator low-shear piston pumps 22 which draw material fromrespective drums 24. Valving 26, 28 is provided for allowing replacementof one material drum while operation continues as the other. Material issupplied under pressure from pumps 22 through conduit 30 to a materialconditioning apparatus 32 for heating the material to an elevatedtemperature for deposition on panel 14, and then by a conduit or hose 34to an extrusion nozzle 36. Nozzle 36 is carried at the end of robot arm18, and in accordance with an important advantage of the presentinvention, material conditioner 32 is of sufficiently small size that italso may be carried on robot arm 18 adjacent to extrusion nozzle 36 forminimizing heat loss in material traveling from conditioner 32 throughconduit 34 to nozzle 36. Material conditioner 32 is connected to acontrol package 38, which includes control electronics to be describedin detail in connection with FIG. 2 and other suitable means forselectively-controlling temperature of material passing throughconditioner 32.

Referring to FIGS. 2 and 3, material conditioner 32 comprises asubstantially cylindrical hollow enclosure 40 having a sidewall 42 and apair of axially opposed endwalls 44, 46. A pair of aligned brackets 48are welded or otherwise affixed at axially spaced positions on enclosuresidewall 42, and a strap 50 is adjustably coupled to each bracket 48 formounting material conditioner 32 on the arm of robot 18. Aspirally-coiled tube 54, of stainless steel tube stock, has amultiplicity of coils 56 at uniform diameter and pitch substantiallyco-axially disposed within the interior 52 of enclosure 40. Tube 54 issuspended within enclosure 40 by the axially-opposed coil inlet andoutlet ends 58, 60. Suitable fittings 62, 64 are carried by endwalls 44,46 and respectively connect tube ends 58, 60 to conduits 30, 34 (FIGS. 1and 2). An electric heater 66 has a base 68 approximately centrallymounted on enclosure endwall 46 and a heater element 70 extendingtherefrom into enclosure interior 52 substantially centrally (in thediametric direction) of coils 56. A temperature sensor 72 has a base 74substantially centrally mounted on enclosure endwall 44, and has atemperature probe 76 extending into enclosure volume 52 substantiallycentrally (in the diametric direction) within tube coils 56. Heater 66and temperature sensor 72 are connected to control electronics 78.

An inlet fitting 80 and an oulet fitting 82 are respectively disposed onendwalls 44, 46 for circulating heat transfer fluid through the hollowinterior 52 of enclosure 40. Outlet fitting 82 is connected to inletfitting 80 by suitable fluid conduits in a closed loop through a chiller84, a pump 86, a solenoid valve 88 and a flow-indicator 90. Chiller 84includes a compressor and suitable refrigerant elements for cooling heattransfer fluid passing therethrough. Chiller 84, pump 86 and solenoidvalve 88 each receive control inputs from controller 78. Controller 78also receives an input from a temperature adjustment mechanism 92 foroperator selection of temperature within enclosure 40 to which epoxypassing through coil 54 is to be raised, and has an output connected tosuitable alarms 94 for indicating over-temperature, under-temperatureand other desired alarm conditions. The heat transfer fluid preferablycomprises a mixture of glycol and water or other medium required byoperating temperature parameters.

In operation, deposition temperature at bead 12 (FIG. 1) is normallyspecified by a process engineer based upon technical data for theparticular material in question, empirical design and operatingexperience, and other factors. Temperature to which the material is tobe raised within conditions 32 is normally set at adjustment 92 at someslightly higher temperature so as to accommodate heat loss in conduit 34and extrusion nozzle 36. For example, if a deposition temperature of100° F. is desired at bead 12, a temperature of 105° F. may be initiallyset at adjustment 92, and thereafter readjusted upwardly or downwardlydepending upon actual measurement process experience, etc. with thetemperature so set, the one-part thermal-cure material, such asstructural epoxy, is then propelled through conditioner 32 underpressure from pumps 22. As the material flows through coils 56, heater66 is operated by controller 78 so as to heat the heat transfer fluidwithin enclosure 40, with the heat transfer fluid conducting such heatenergy to coils 56 and then to the epoxy material. Temperature probe 72provides electronic signals to controller 78 indicative of heat transferfluid temperature. Controller 78, which preferably comprises amicroprocessor-based controller, contains suitable programming foroperating chiller 84, pump 86, solenoid valve 88 and heater 66 tomaintain the heat transfer fluid within enclosure 40 surrounding coils54 at the desired operating temperature.

In accordance with the an important advantage of the present inventioncoiled tubing 54 inherently automatically folds the epoxy material onitself during passage therethrough, which helps enhance heatdistribution throughout the material without imparting shear stresses tothe material that might undesirably activate material thixotropes. Suchuniform heat distribution without shear is thus important in obtainingand maintaining desired properties in the epoxy material. Length ofcoiled tubing 54 within enclosure 40 is selected to provide sufficientmaterial residence time within conditioner 32 for uniform heating andtemperature increase, given the material flow rate prespecified by theprocess engineer. It has been empirically determined in development ofthe present invention that an optimum material residence time withinconditioner 32 is equal to approximately 3.2 times material flow rate inhours. For example, if flow rate is specified at twenty-five cubicinches per hour, length and internal diameter of coil 54 are selected tohold eighty cubic inches of epoxy. Coil pitch is selected as a balancebetween back pressure of fluid resulting from reduced pitch andincreased axial length of enclosure 40 necessitiated by greater pitch.

What is claimed is:
 1. A system for applying a fluent .[.thermal-cure.].material to a substrate that includes means for supplying the materialunder pressure, means for heating the material to elevated temperatureabove ambient means for applying the material at said elevatedtemperature to a substrate, and conduit means for feeding the materialfrom said supplying means to said heating means and thence to saidapplying means, characterized in that said means for heating thematerial comprises:a hollow enclosure having a substantially cylindricalinternal volume, a spirally coiled tube having axially opposed first andsecond ends suspending said tube substantially coaxially with saidvolume and being coupled to said conduit means, a heater positionedwithin said enclosure and having means responsive to application ofelectrical power for heating said volume, temperature sensing meanspositioned within said volume for supplying electronic signals as afunction of temperature thereof, said heater and said temperaturesensing means being positioned within said coiled tube substantiallycentrally of said volume and said tube, and electronic control meansincluding means responsive to said electronic signals for selectivelyapplying electrical power to said heater to maintain temperature withinsaid volume at said elevated temperature.
 2. The system set forth inclaim 1 wherein said heater comprises an elongated heating elementextending from one end of said enclosure substantially centrally of saidcoiled tube.
 3. The system set forth in claim 2 wherein said coiled tubecomprises coils of uniform diameter and pitch.
 4. The system set forthin claim 3 adapted for applying the material at a predetermined constantflow rate, wherein said supplying means includes a pump for supplyingthe material at said predetermined constant flow rate, and wherein saidcoiled tube has a diameter and length selected to provide apredetermined residence time of material in said heating means at saidpredetermined flow rate.
 5. The system set forth in claim 4 wherein saidresidence time is substantially equal to 3.2 hours.
 6. The system setforth in claim 5 wherein said electronic control means further comprisesmeans for selectively adjusting temperature within said volume.
 7. Thesystem set forth in claim 3 wherein said heating means further comprisesa heat transfer fluid within said volume for enhancing heat transferfrom said heater to said coiled tube.
 8. The system set forth in claim 7wherein said heating means further comprises means for circulating saidheat transfer fluid externally of said enclosure.
 9. The system setforth in claim 8 wherein said heat transfer fluid comprises a mixture ofglycol and water.
 10. The system set forth in claim 8 wherein saidcirculating means comprises means forming a fluid inlet and a fluidoutlet at opposed ends of said volume.
 11. The system set forth in claim8 wherein said circulating means comprises means coupled to saidelectronic control means for selectively cooling said heat transferfluid.
 12. The system set forth in claim 11 wherein said electroniccontrol means comprises microprocessor=based control means includingmeans responsive to said electronic signals selectively to operate saidheater and said cooling means to maintain said heat transfer fluid atsaid elevated temperature.
 13. The system set forth in claim 1 whereinsaid heating means further comprises a heat transfer fluid within saidvolume for enhancing heat transfer from said heater to said coiled tube.14. The system set forth in claim 13 wherein said heating means furthercomprises means for circulating said heat transfer fluid externally ofsaid enclosure.
 15. The system set forth in claim 14 wherein said heattransfer fluid comprises a mixture of glycol and water.
 16. The systemas set forth in claim 1 wherein said means for applying the materialcomprises an extrusion nozzle.
 17. A system for applying a fluent.[.thermal-cure.]. material to a substrate that includes means forsupplying the material under pressure, means for heating the material toelevated temperature above ambient, means for applying the material atsaid elevated temperature to a substrate, and conduit means for feedingthe material from said supplying means to said heating means and thenceto said applying means, characterized in that said means for heating thematerial comprises:a hollow enclosure having an internal volume, aspirally coiled tube suspended within said enclosure and having firstand second tube ends coupled to said conduit means, a heater positionedwithin said enclosure and having means responsive to application ofelectrical power for heating said volume, temperature sensing meanspositioned within said volume for supplying electronic signals as afunction of temperature thereof, electronic control means includingmeans responsive to said electronic signals for selectively applyingelectrical power to said heater to maintain temperature within saidvolume at said elevated temperature, a heat transfer fluid within saidvolume for enhancing heat transfer from said heater to said coiled tube,and means for circulating said heat transfer fluid externally of saidenclosure.
 18. The system set forth in claim 17 wherein said enclosurevolume is substantially cylindrical, said spirally coiled tube havingaxially opposed ends suspending said tube within said volume and beingcoupled to said conduit means.
 19. The system set forth in claim 18wherein said coiled tube is suspended so as to have an axissubstantially in the center of said volume, said heater and saidtemperature sensing means being positioned within said coiled tubesubstantially centrally of said volume and said tube.
 20. The system setforth in claim 17 wherein said circulating means comprises means forminga fluid inlet and a fluid outlet at opposed ends of said volume.
 21. Thesystem set forth in claim 20 wherein said circulating means comprisesmeans coupled to said electronic control means for selectively coolingsaid heat transfer fluid.
 22. The system set forth in claim 21 whereinsaid electronic control means further comprises means for selectivelyadjusting temperature within said volume.
 23. The system set forth inclaim 22 wherein said electronic control means further comprisesmicroprocessor-based control means including means responsive to saidelectronic signals selectively to operate said heater and said coolingmeans to maintain said heat transfer fluid at elevated temperature. 24.The system set forth in claim 1 adapted for applying the material at apredetermined constant flow rate, wherein said supplying means includesa pump for supplying the material at said predetermined constant flowrate, and wherein said coiled tube has a diameter and length selected toprovide a predetermined residence time of material in said heating meansat said predetermined flow rate.
 25. The system set forth in claim 24wherein said pump is a piston pump.
 26. The system as set forth in claim24 wherein said residence time is substantially equal to 3.2 hours.